He was 9 years old when his mother woke him before dawn half a century ago in Cold War America. Eric Olson came blinking into the living room of their Frederick, Md., home, where his father's boss and friend, Col. Vincent Ruwet, sat with the family doctor.

"Everybody had this stony-faced expression," Olson recalls. "I remember Ruwet saying, 'Your father was in New York and he had an accident. He either fell out the window or jumped.' "

After decades of dogged inquiry, Eric Olson now has a new verb for what happened to his father, Frank Olson, who worked for the Army's top-secret Special Operations Division at Fort Detrick, where he developed bioweapons and experimented with mind-control drugs.

Eric Olson found the verb in a 1950s CIA manual that was declassified in 1997 -- one more clue in a quest that has consumed his adult life.

The verb is "dropped." And the manual is a how-to guide for assassins.

"The most efficient accident, in simple assassination, is a fall of 75 feet or more onto a hard surface," the manual says, adding helpfully: "It will usually be necessary to stun or drug the subject before dropping him."

Eric Olson believes his father -- who developed misgivings about his work and tried to resign -- was murdered by government agents to protect dark government secrets.

To find out what happened in the Statler Hotel on the night of Nov. 28, 1953, Eric once spent a sleepless night in the room from which his father fell. He confronted his father's close-mouthed colleagues. He had his father's mummified body exhumed. And he built a circumstantial case that Frank Olson was the victim of what he calls a "national security homicide."

The government has long denied the charge of murder. But it has admitted what might be called negligent manslaughter. Its version: that Frank Olson crashed through the window in a suicidal depression nine days after he was given LSD without his knowledge in a CIA mind-control experiment.

Eric never bought that argument. His devotion to the case derailed a promising career as a clinical psychologist that began with a doctorate from Harvard. In some Frederick circles, you'll hear disapproving murmurs about Eric's obsession -- contrasted with the success of his younger brother, Nils, a dentist. But Nils Olson, 55, says he admires his brother's tenacity and agrees with his conclusion.

"At every point there seems to be a convergence of the evidence," Nils Olson says. "It all points to my father's being murdered."

The patriotic community surrounding Fort Detrick has long been reluctant to believe such a possibility. Once, Eric Olson says, he was, too.

"I'm not essentially conspiratorial in my world view," says the lanky psychologist, who seems almost boyish at 59. "In my father's case, I just started turning over stones, and there was a snake under every one."

It may well be that Olson is wrong -- that the government merely drugged his father with LSD, treated him thoughtlessly when he fell into madness and covered it up for 22 years. But if Frank Olson was murdered, then part of the plan would naturally be a cover-up.

"No assassination instructions should ever be written or recorded," says the CIA assassination manual. "Decision and instructions should be confined to an absolute minimum of persons."

It adds: "For secret assassination the contrived accident is the most effective technique. When successfully executed, it causes little excitement and is only casually investigated."

Whether the truth is homicide or suicide induced by a reckless drug experiment, the Olson saga is a cautionary tale in an era that echoes the early days of the Cold War. In the war on terror, America again appears tempted to use extreme measures.

In Olson's case, it took the government until 1975 to admit to the LSD experiment. When an investigation of CIA abuses exposed the facts in 1975, two White House aides named Dick Cheney and Donald Rumsfeld helped set up a meeting at which President Gerald Ford apologized to the Olson family.

The goal, according to a declassified White House memo, was to avert a lawsuit in which it "may become apparent that we are concealing evidence for national security reasons."

What evidence was concealed, the memo does not reveal. But people who are far from wild-eyed conspiracy theorists accept the plausibility of Frank Olson's death as an execution.

Among them is Army intelligence veteran Norman G. Cournoyer, 85, who worked with Olson at Detrick and became one of his closest friends.

"To shut him up," Cournoyer says. "Frank was a talker. His concept of being a real American had changed. He wasn't sure we should be in germ warfare, at the end."

William P. Walter, 78, who supervised anthrax production at Detrick, says Olson's colleagues were divided about his death. "Some say he jumped. Some say he had help," Walter says. "I'm one of the 'had-help' people."

So is James Starrs, a George Washington University forensic pathologist who examined Olson's exhumed corpse in 1994 and called the evidence "rankly and starkly suggestive of homicide."

Based on that finding, the Manhattan district attorney's office opened a homicide investigation in 1996. Two cold-case prosecutors, Steve Saracco and Daniel Bibb, conducted dozens of interviews, hunted records at the CIA and went to California with a court order to question CIA retiree Robert V. Lashbrook, who shared Olson's room the night he died. (Like everyone known to be directly involved, Lashbrook is now dead.)

In 2001, they gave up.

"We could never prove it was murder," says Saracco.

But Saracco, now retired, found plenty to fuel his suspicions: a hotel room so cramped it was hard to imagine Olson vaulting through the closed window; motives to shut Olson up; the ambiguous autopsy; and the CIA assassination manual.

"Whether the manual is a complete coincidence, I don't know," Saracco says. "But it was very disturbing to see that a CIA manual suggested the exact method of Frank Olson's death."

In 1949, Olson was recruited by Detrick's Special Operations Division. Within months, the Korean War was raging, Sen. Joseph McCarthy was launching his hunt for Communist agents, and pressure was on to build new U.S. germ weapons.

In October 1952, Olson was promoted to acting director of the division. Although his family didn't know it, he had also been recruited by the CIA for a program code-named Artichoke, part of a decades-long hunt for drugs to make enemy prisoners spill their secrets.

As his career prospered, Olson and his wife, Alice, built a dream house on a hillside above Frederick. They became regulars at Detrick's officers' club.

But promotions and parties concealed Olson's qualms about his work. Suffering from ulcers, he left the Army and stayed on at Detrick as a civilian -- though he bridled at the Army's strict oversight. A 1949 security document reported: "Olson is violently opposed to control of scientific research, either military or otherwise, and opposes supervision of his work."

The same year, colleagues recall, Olson was influenced by a new book by a mentor. "In Peace or Pestilence: Biological Warfare and How To Avoid It," Theodor Rosebury said science should combat disease, not find devious ways to spread it.

Cournoyer, the Army intelligence veteran, says Olson began to raise ethical issues the friends had discussed during night courses in philosophy at the Catholic University of America. Colleagues were astonished to spot Olson chatting with the pacifists who protested outside Detrick's gates.

"He was turning, no doubt about it," Cournoyer says.

Whatever its source, Olson's disillusionment came to a head after the LSD experiment on Nov. 19, 1953, at a rented cabin on Deep Creek Lake in western Maryland. Olson -- who had stepped down to deputy chief of Special Operations -- joined six Army colleagues and three CIA men led by Sidney Gottlieb, the eccentric and powerful CIA liaison to Detrick.

By his own account, Gottlieb served Cointreau to seven of the men without telling them he had laced it with LSD, ostensibly to study the drug's effects.

Alice Olson would recall that her husband returned home deeply depressed. He told her he had made a "terrible mistake" but wouldn't elaborate. He said he planned to leave the Army and retrain as a dentist.

According to the official CIA version of events, made public in 1975, Olson became increasingly despondent and paranoid. On Nov. 24, concerned colleagues took him to New York to see a doctor, Harold Abramson, who had experimented with LSD.

Three days later, Olson agreed to be admitted to a Rockville psychiatric hospital. He and CIA officer Robert Lashbrook decided to spend the night at the Statler and head south the next morning.

But at 2:45 a.m., Lashbrook told investigators, he awoke to the sound of breaking glass. Olson had thrown himself through the closed shade and closed window, falling 170 feet to his death on the sidewalk below.

From 1953 to 1975, as Alice Olson descended into alcoholism and fought back to sobriety, she and her children were told nothing about LSD. When the story finally surfaced in the Rockefeller Commission report on CIA abuses, they received official apologies from President Ford and from CIA Director William Colby, who handed over CIA documents on the case. They later received $750,000 in compensation.

But 22 years of deception made it difficult to persuade the family that the new official story was the whole truth.

The betrayal was deeply personal. The LSD cover-up had involved Frank Olson's colleagues, particularly his boss, the late Col. Vincent Ruwet -- who had consoled Eric with the gift of a darkroom set and a jigsaw after his father's death.

"Whenever suspicions came up, the family would say: 'This can't be correct, because Ruwet would have known, and Ruwet wouldn't deceive us.' Our relationship to Ruwet was symbolic of our relationship to the whole Detrick community," Eric said.

As a teenager, Eric was a patriotic member of that community, where he became an Eagle Scout in the base-sponsored troop. But in college and graduate school, he grew skeptical.

If his mother shared his doubts, Eric said, she never acted on them: "My mother's mantra was: 'You are never going to know what happened in that hotel room.' It's an injunction, a kind of threat, a taboo and a prediction."

Eric's younger sister, Lisa, was killed in a 1978 plane crash along with her husband and 2-year-old son. Ironically, she died on the way to inspect a lumber mill as a place to invest her share of the government's compensation for Frank's death.

His brother, Nils, who was only 5 in 1953, consciously chose dentistry, the alternate career his father had considered.

But Eric, the eldest, couldn't settle down. He moved to Sweden, his father's ancestral home, and had a son, Stephan, with a Swedish woman. Then he returned to the family home, determined to explain his father's death.

One clue came from Armand Pastore, the assistant night manager at the Statler in 1953. He approached the family in 1975 to report what he'd heard from the hotel switchboard operator that night. Immediately after Olson's fall, CIA officer Lashbrook phoned Abramson, the physician. Instead of shocked and emotional voices, the operator had told Pastore, there was a brief and seemingly expected exchange.

"He's gone," Lashbrook said.

"That's too bad," Abramson reportedly answered.

A similar impression came from a CIA investigator's report in Colby's documents. Dispatched to New York immediately after Olson's death, the investigator listened through a closed door as Abramson told Lashbrook he was "worried as to whether or not the deal was in jeopardy" and thought "the whole operation was dangerous and the whole deal should be reanalyzed."

In a report to the CIA on the death, Abramson wrote that the LSD experiment was designed "especially to trap (Olson)." This conflicted with Gottlieb's story and raised a troubling possibility: that the LSD experiment was actually designed to see whether Olson could still be trusted to keep the agency's dark secrets.

And there was Frank Olson's mummified body, exhumed in 1994, the year after Alice Olson died. Starrs, the pathologist, found none of the facial cuts the original autopsy described, but he did find a contusion to the head that he thought was caused by a blow struck before the fall.

A half-century after his father's death, Eric Olson seems to be struggling to put it behind him. He says he believes he knows what happened, even if he doesn't know details of perpetrators and motives. "You can see the truth through the fog," he says. "But you can't quite make out what it is."

Sometimes, in moments of frustration -- which come often because he's struggling to earn a living -- he says he's sorry he ever looked into his father's death.

"I've ruined my life," he says in one interview. "I regret everything. I regret digging my father's body up. For me, the end has come with facing a hard truth, confronting my own naivete. I thought I wanted knowledge. I didn't think that if knowledge is knowledge of murder, then it's not enough -- because then you want justice. And you don't get justice with a secret state murder."

At other times, he seems eager for any new scrap of information. He explains the contradiction by citing the Shakespearean son who pursues the truth about his father's murder.

"Read 'Hamlet,' " he says. "Hamlet has become like a friend to me. Once you start looking into your father's death, you go to the end."